I love ADW Launcher. Sick amount of customization for your home screen. And free, which is nice. (buy an add-on to support the dev. He deserves it.)
Note Everything Pro for lists, checklists, and note taking. Bought the pro version for the ability to stick notes in the notification bar and checklists.
Android Agenda Widget for keeping track of important dates, tasks, and work stuff. It displays multiple calendars and my Google Tasks when its integrated with...
Dato GTasks. Nuff said.
Quick Profiles. Allows control over volume, ringtones, screen brightness with one click. Handy when going from home to the cubicle to a meeting. Also, I can finally switch my humorous work ringtone and a sedate home ringtone with a touch. The work ringtone scared my kids (its the Gorillaz "M1A1" sample from Dawn of the Dead...)